GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: Tack Driver 10 on August 14, 2024, 02:05:15 PM
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This is a gun I built 5 years ago.
It's a 5th variant 760, manual cocking, made 77-80.
Metal receiver with brass cocking bolt.
Nice simple well made gun, perhaps the best of the 760 litter.
It has an adjustable 90A poly cone piston.
The valve volume is reduced and the headspace minimized.
Has a 21 1/2" 2100 soda straw barrel encased in a carbon fiber tube.
Ran it over the chrony with 7.9 CPHPs:
10 pumps 723 FPS, 09.17 FPE
15 pumps 833 FPS, 12.17 FPE
That's the same velocity it made originally.
I'm going to experiment with it.
Not sure how much more I can squeeze out of it.
Would be nice to get 10 FPE with 10 pumps.
A FT piston/valve should bump up the power some.
Need to improve the trigger.
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Nice job on the Mods and Restoration.
Making 12 fpe with a simple 1 lever pump arm ( Non Compound ) is a pretty good deed done.
Use it and enjoy for what it is 8)
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Nice job on the Mods and Restoration.
Making 12 fpe with a simple 1 lever pump arm ( Non Compound ) is a pretty good deed done.
Use it and enjoy for what it is 8)
Thanks Motorhead.
The valve uses the cap from a 2100 valve so has very little dead air.
Might be able to upgrade the valve stem material depending on what's in there now.
Going to replace the aluminum section on the valve with brass.
May not be worth it to FT the gun if some valve mods work out.
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Need to see how much difference the poly cup piston makes vs a stock piston.
Replaced the adjustable poly cup piston with the center piston.
With 7.9 CPHPs:
10 pumps 670 vs 723 FPS, 07.80 vs 09.17 FPE
15 pumps 762 vs 833 FPS, 10.18 vs 12.17 FPE
Velocity difference would be closer if the stock piston was adjustable.
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The main link pivot had some play so drilled and bushed it.
Normal wear for 45 years of faithful service, I've seen a lot worse.
Drilled it to .236" with a carbide end mil and pressed in a custom .240" bushing.
Slathered the area with JB-Weld prior to pressing in the bushing.
The bushing is 624 Nickel Aluminum Bronze, very strong and durable material.
The spacer ring is standard 360 brass.
Should be good for another 45 years.
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Very nice job on the pivot link play 8). You are not very far from 10 FPE now. If anyone can squeeze out another pound of energy... it would be you! ;)
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following closely...
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Very nice job on the pivot link play 8). You are not very far from 10 FPE now. If anyone can squeeze out another pound of energy... it would be you! ;)
I have extra pump links but rebuilding this one makes it better than new.
The brass spacer builds the width out to .250".
Solid as a rock even with the plastic barrel band.
Pulled the valve and traded the aluminum back half for brass.
Pinned the valve to the tube with 2 Prod screws.
The front of the valve was shaped different than a stock valve.
The poly cone is machined to match.
The stock plastic piston was not a good match, probably why it lost some velocity.
The original valve internals used a balanced configuration.
Replaced it with a conventional setup with a concave seat and peek stem.
Initially tested power with a stock bolt/probe.
The pellet skirt hung halfway into the TP opening.
Modified the stock probe with an extended brass section.
Fully seats the pellet deep into the rifling.
Drilled and tapped the receiver screw holes straight through.
Replaced the tapered self tapping originals with 1" SS phillips head screws.
Put the gun together this morning and ran it over the chrony.
With 7.9 CPHPs:
05 pumps 543 FPS, 05.17 FPE
07 pumps 641 FPS, 07.21 FPE
10 pumps 757 vs 723 FPS, 10.05 vs 09.17 FPE
With 10.65 Barracuda Match
10 pumps 673 FPS, 10.71 FPE
Need to fix the trigger and hammer strike.
I can hear the hammer double tap when fired.
Nature of the beast with the 760 due to it's 1" cocking length and long weak spring.
Might be able to coax a little more power yet, the fun continues......
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That didn't take long, lol 8). What barrel is on it? I see a carbon fiber pattern... FX?
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That didn't take long, lol 8). What barrel is on it? I see a carbon fiber pattern... FX?
The gun was close just needed some updates.
The barrel is a soda straw barrel from a 2100 with a carbon fiber sleeve.
Modified the hammer.
Added a brass sleeve to the front.
It removes most of the creep in the trigger and makes it a 2 stage trigger.
Pull went from 2 1/2 lbs to 12 oz.
The brass spring guide makes the spring stronger.
Drilled the hammer and pressed in 1/8" Delrin skid pads.
Stock hammer weighs 30 grams, modified weighs 34 grams.
Gun cocks nice and smooth and dumps all the air.
Could use more valve volume but a good 10-12 pump gun as is.
With 7.9 CPHPs:
10 pumps 757 FPS, 10.05 FPE unchanged
12 pumps 800 FPS, 11.22 FPE
15 pumps 852 FPS 12.73 FPE
With 10.65 Barracuda Match
15 pumps 755 FPS 13.48 FPE
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The hammer updates look great and it appears to be kicking out some awesome power! 8)
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The hammer updates look great and it appears to be kicking out some awesome power! 8)
Right, the gun's making great power with the custom profiled valve/poly cup.
I'm going to replace the front valve section with a more pedestrian solution.
Using a 2100 valve cap on a chop top valve front end.
This will place the check all the way to the front.
Essentially an extended length 2100 valve in a 760.
Have a modified 362 piston head similar to the one in your 362. (look familiar?)
The "Chameleon" can be a cup seal or flat top, two heads really are better than one.
The black cup is a stock cup, the other 2 cups are poly with a stock profile.
There's also the option of testing a FT piston/valve.
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Yes it does ;D. Loving mine along with that amazing valve you made. 8)
You definitely have some options there. Looking forward seeing more results ;).
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Took the gun apart and swapped valve fronts/pistons.
Same valve internals, the 2100 cap reduces the valve volume by .030".
Results are marginally higher perhaps due to the reduced valve volume.
With 07.9 CPHPs:
05 pumps 553 FPS, 05.36 FPE
07 pumps 662 FPS, 07.70 FPE
10 pumps 757 FPS 10.05 FPE
12 pumps 805 FPS, 11.37 FPE
15 pumps 860 FPS 12.97 FPE
With 13.4 FX
10 pumps 614 FPS 11.22 FPE
15 pumps 704 FPS, 14.74 FPE
Previous tests revealed the poly cup and HP FT performed better than the stock cup.
Need to try one of the poly cup pistons with the 2100 cap valve front.
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Tried one of the poly pistons but only made 5-10 more FPS.
Reinstalled the 362 piston head.
I'm going to keep it simple for now.
If anything may give it some more valve volume.
These V5 760s won't allow you to de-cock the gun.
Easy fix is to cut the post on the trigger back so it's even with the sear.
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15 pumps 704 FPS, 14.74 FPE
My mind is blown. If i would have that as a child i would have grown up to be a neurosurgeon, would have found the cure for cancer and built the first beach house in Mars. But no, i got stuck with a 5 fpe 760, that turned into bigger guns, years in the military and a long stint at the GTA...
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15 pumps 704 FPS, 14.74 FPE
My mind is blown. If i would have that as a child i would have grown up to be a neurosurgeon, would have found the cure for cancer and built the first beach house in Mars. But no, i got stuck with a 5 fpe 760, that turned into bigger guns, years in the military and a long stint at the GTA...
My first and only airgun as a kid was an early 1st gen 760.
Had to pump them 25 times to make max power as per the OM.
This gun makes great power but it does get harder to pump above 10 pumps.
I'm calling it a 10 pump gun with a emergency reserve of 15 pumps.
Modified a spare hammer adding weight and extending the length .500".
Added a .322" spacer in the hammer so can now use a 13xx hammer spring.
The 13xx spring is shorter but stiffer.
This also reduces the distance it takes to cock the gun from 1" to about .5".
Should get a chance to test it in the morning.
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dude, that manual states 25 pumps its ok! Printed before political correcteness was invented, before we stopped having TV heroes that smoked cigarettes, when it was ok to compliment a nicely dressed lady!
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Oh wow! An actual honest to goodness Informative instruction book that's large enough in print to actually be read. Those were the days. ;)
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Been experimenting with the gun for the last few days.
Gun sounds like it's in burst mode when fired.
The hammer is making multiple strikes on the valve stem.
Reduced the valve bumper from .400" to .340" to solve the problem.
Stem travel is .160" vs .100 prior.
Trimmed the hammer .100" so now weighs 44 grams vs 50.
Hammer travel is .700" from full cocked to where it contacts the stem.
Swapped the 13xx hammer spring for a cut 2100 spring.
Added valve volume so the gun could be pumped to 21 strokes.
The increased volume will lower the velocity at the low end some.
With 07.9 CPHPs:
05 pumps 541 vs 553 FPS, 05.13 vs 5.36 FPE
10 pumps 740 vs 757 FPS, 09.60 vs 10.05 FPE
12 pumps 784 vs 805 FPS, 10.78 vs 11.37 FPE
15 pumps 848 vs 860 FPS, 12.61 vs 12.97 FPE
21 pumps 943 vs n/t FPS, 15.60 FPE
With 13.4 FX/JSB
15 pumps 694 vs 704 FPS, 14.33 vs 14.74 FPE
21 pumps 777 vs n/t FPS, 17.96 FPE
Gun is making good power, comparable to an HP 2100 made 10 years ago.
Need to make a custom probe.
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You didn't really very much power in either velocity or energy.
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You didn't really very much power in either velocity or energy.
Not a big drop but it did allow the gun to be pumped higher.
Made the new probe and will retest this weekend.
More pictures of the mods: